Battery cells in a battery pack are generally not completely identical. Individual battery cells in a battery pack may tend to operate at different temperatures and voltages even though the individual battery cells are of the same model and time-in-service. Non-uniformity in the voltage among individual battery cells has been balanced using resistive loads. The energy dissipated by the resistive loads is generally wasted energy. The service life of a battery may be deleteriously affected by operation outside of a normal operating temperature band.